1. Field of the Invention
The present invention relates to golf balls which have an outstanding flight performance, an excellent scuff resistance and a soft xe2x80x9cfeelxe2x80x9d upon impact.
2. Prior Art
Golf balls have hitherto been modified and improved in a variety of ways to address the numerous and diverse requirements of golfers. The present assignee, among others, has already disclosed many outstanding golf balls.
For example, JP-A 9-313643 describes an all-round golf ball which has excellent flight characteristics and durability, a good, soft feel on impact, and controllability.
JP-A 10-305114 discloses a golf ball having a dramatically increased carry and a good feel on impact.
JP-A 11-114094 teaches a golf ball in which deflection by the solid core and the relative thicknesses and hardnesses of the cover and the mantle have been optimized so to provide a good trajectory and increased carry on shots with a driver, suitable spin characteristics and good controllability on approach shots, and excellent feel on impact and durability.
JP-A 2000-225209 relates to golf balls with an excellent overall performance that have the feel, durability and rebound characteristics required of a ball construction subject to limitations with respect to solid core deformation, hardness of the cover and the mantle and dimple characteristics, and that also have excellent flight characteristics.
JP-A 2001-218873 describes a golf ball of outstanding feel, controllability and flight performancexe2x80x94including carry, in which the mantle and/or cover are formed of specific materials, and in which the respective Shore D hardnesses of the solid core center and surface and of the mantle and the cover are such as to satisfy the following relationship: solid core center hardnessxe2x89xa6mantle hardnessxe2x89xa6cover hardness.
JP-A 2002-210042 discloses a golf ball having a very soft feel on impact yet good durability and also having a low spin, high angle of elevation and high rebound that together provide increased carry. This prior-art golf ball is achieved by specifying all of the following: center hardness, surface hardness and diameter of the solid core, mantle hardness, thickness and material, cover hardness, thickness and material, difference in hardness between mantle and solid core surface, difference in hardness between cover and mantle, relationship between hardness gradient from mantle to cover and hardness gradient from center of core to mantle, and dimple arrangement.
JP-A 8-276033 teaches a way of obtaining a solid golf ball having a good feel on impact and a long carry by setting the difference A-B between the compression deflection A by the core when subjected to a final load of 130 kgf from an initial load of 10 kgf and the compression deflection B by the ball when subjected to a final load of 130 kgf from an initial load of 10 kgf within a specific range.
These prior-art golf balls all have an excellent feel and an excellent carry and other flight characteristics, and can be suitably adapted to various requirements dictated by the skill level of the golfer and the intended use of the ball (e.g., recreational or competitive). Yet, given the ever-high expectations of golfers, there exists a need for golf balls endowed with an even better performance.
It is therefore an object of the present invention to provide golf balls which have excellent flight characteristics and scuff resistance, and which also have a soft feel on impact.
We have found that multi-piece solid golf balls constructed of a solid core, a mantle of at least one layer and a cover can be conferred with better flight characteristics, a higher scuff resistance and a softer feel on impact than prior-art golf balls by having the solid core made of a specific rubber composition and endowed with a specific degree of flexibility and diameter, having the mantle made of a specific thermoplastic resin composition and endowed with a specific thickness and hardness, having the cover made of a specific resin composition and endowed with a specific thickness and hardness, and setting the flexibility of the overall golf ball within a specific range.
Accordingly, this invention provides a multi-piece solid golf ball constructed of a solid core, a mantle of at least one layer which encloses the core, and a cover which encloses the mantle, wherein the solid core is made of a rubber composition comprising (A) 100 parts by weight of a base rubber that contains 60 to 100 wt % of a polybutadiene of at least 60% cis-1,4 structure and synthesized using a rare-earth catalyst, (B) 0.1 to 0.8 part by weight of an organic peroxide, (C) an unsaturated carboxylic acid and/or a metal salt thereof, (D) an organic sulfur compound and (E) an inorganic filler, has a deflection when subjected to a load of 980 N (100 kgf) of 3.0 to 6.0 mm, and has a diameter of 30 to 40 mm; the mantle of at least one layer is made of a thermoplastic resin composition, has a thickness per layer of 0.5 to 2.0 mm, and includes an outermost layer which is in contact with the cover and has a Shore D hardness of 20 to 60; the cover is made of a material composed of a heated mixture of (F) at least one selected from the group consisting of olefin/unsaturated carboxylic acid copolymers, olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester copolymers and metal ion neutralization products thereof, (G) a polyurethane elastomer and (H) an organic or inorganic basic compound, has a thickness of 0.5 to 2.5 mm and a Shore D hardness of 50 to 70, and satisfies the condition (Shore D hardness of mantle outermost layer)xe2x89xa6(Shore D hardness of cover); and the golf ball has a deflection when subjected to a load of 980 N (100 kgf) of 3.0 to 5.0 mm.
The polybutadiene is typically a modified polybutadiene prepared by synthesis using a neodymium catalyst, followed by reaction with a terminal modifier.
Preferably, the rubber composition includes (A) 100 parts by weight of a base rubber containing 60 to 100 wt % of a polybutadiene of at least 60% cis-1,4 structure and synthesized using a rare-earth catalyst, (B) 0.1 to 0.8 part by weight of at least two kinds of organic peroxide, (C) 10 to 60 parts by weight of an unsaturated carboxylic acid and/or a metal salt thereof, (D) 0.1 to 5 parts by weight of an organic sulfur compound, and (E) 5 to 80 parts by weight of an inorganic filler.
According to one preferred embodiment, the thermoplastic resin composition making up the mantle is composed of 100 parts by weight of resin components which include a base resin of (P) an olefin/unsaturated carboxylic acid binary random copolymer and/or a metal ion neutralization product of an olefin/unsaturated carboxylic acid binary random copolymer in admixture with (Q) an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester ternary random copolymer and/or a metal ion neutralization product of an olefin/unsaturated carboxylic acid/unsaturated carboxylic acid ester ternary random copolymer in a weight ratio P/Q of 100:0 to 25:75, and (R) a non-ionomeric thermoplastic elastomer in a weight ratio (P+Q)/R of 100:0 to 50:50; (S) 5 to 80 parts by weight of a fatty acid or/or fatty acid derivative having a molecular weight of 280 to 1,500; and (T) 0.1 to 10 parts by weight of a basic inorganic metal compound capable of neutralizing un-neutralized acid groups in the base resin and component S.
According to another preferred embodiment, the thermoplastic resin composition making up the mantle is a polyester elastomer.
Preferably, the mantle consists of an inner layer and an outer layer.
Typically the golf ball cover bears a plurality of dimples on a surface thereof. Each dimple has a spatial volume below a planar surface circumscribed by an edge of the dimple and having a surface area circumscribed by the dimple edge on a hypothetical sphere represented by the surface of the golf ball cover were it to have no dimples. It is preferable for the golf ball to have a dimple volume occupancy VR, defined as the ratio of the sum of the individual dimple volumes to the volume of the hypothetical sphere, of 0.70 to 1.00%, and a dimple surface coverage SR, defined as the ratio of the sum of the individual dimple surface areas to the surface area of the hypothetical sphere, of 70 to 85%.